Ultra-short laser beam pulses are required in a variety of scientific and engineering applications. The literature generally defines ultra-short laser beam pulses as pulses with a half-amplitude duration of less than about one hundred picoseconds. This definition shall apply in the present specification.
In most prior art methods for the generation of ultra-short laser pulses, long pulse trains are produced, each ultra-short pulse having a pulse width of a few nanoseconds or less, corresponding to the period of the laser resonator. However, a number of applications require radiation pulse trains in which the individual ultra-short pulses follow each other at relatively large intervals; typically, those intervals may correspond to a pulse sequence frequency of approximately one Hertz to 20 kHz. Such impulse trains, with pulse sequence frequencies of less than one mHz, especially below 100 kHz, are designated as consisting of "individual" ultra-short pulses. To obtain such individual ultra-short pulses from the above-mentioned impulse trains, from impulse sequence frequencies of about 100 mHz or less, using prior art techniques, expensive electro-optical or acoustical-optical devices have been required because the ultra-short individual pulses cannot be generated directly.
Actually, one known system can be employed to generate individual sub-nanosecond pulses, using a dye laser of appropriate wavelength pumped by short pulses from a nitrogen laser. However, this known method only permits the generation of laser pulses whose half-amplitude duration is far above 100 psec, even by going to the limit of the technical possibilities with respect to the shortening of the pulse width.